Improvement of nanocrystalline diamond film growth process using pulsed Ar/H₂/CH₄microwave discharges

Abstract

For the first time nanocrystalline diamond (NCD) films were deposited by the pulsed microwave plasma assisted chemical vapour deposition process starting from an Ar/H2/CH4 gas mixture. Comparisons with continuous mode deposition gave evidence for the improvement in film quality when the microwave power was modulated with a pulse repetition rate in the range 50–1000 Hz. A reduction in grain size and surface roughness, especially at low pulse repetition rate, accompanied by a decrease in soot particle formation was observed. A thermo-chemical plasma model, developed for pulsed Ar/H2/CH4 microwave discharges, provides evidence for the fact that the pulsed mode permits the enhancement of the mole fraction of the C2 dimer assumed to be the growth precursor of NCD. This may be responsible for a high secondary nucleation rate improving the nanostructure of the film in pulsed discharges.